Acute cold stress modulates metabolic, antioxidant, and immune responses in the skin of juvenile yellowfin tuna (Thunnus albacares)

This study investigated the effects of acute cold stress on metabolic, antioxidant, and immune responses in the skin tissue of juvenile yellowfin tuna ( Thunnus albacares ). Fish were exposed to three temperature treatments (30, 24, and 18 °C), with sampling conducted at 0, 12, 24, and 36 h. During early cold exposure, the relative enzymatic capacities of lactate dehydrogenase (LDH) and alanine aminotransferase (ALT) increased under standardized assay conditions, accompanied by upregulation of hexokinase ( hk ) and ATPase Na + /K + -transporting subunit beta 1a ( atp1b1a ) gene expression. Cold stress was associated with oxidative stress-related responses, as indicated by elevated malondialdehyde (MDA) content, increased catalase (CAT) activity and transient upregulation of superoxide dismutase 2 ( sod2 ), glutathione peroxidase 1a ( gpx1a ), and nuclear respiratory factor 1 ( nrf1 ) gene expression. Immune-related genes, including interleukin-1 beta ( il-1β ), nuclear factor kappa B subunits 1 and 2 ( nfkb1 and nfkb2 ), and tumor necrosis factors alpha and beta ( tnf-α and tnf-β ), were also upregulated during early exposure. As low-temperature exposure was prolonged, various key indicators, including the relative enzymatic capacities of LDH, ALT, CAT, and glutathione peroxidase (GSH-Px), as well as gpx1a , il-1β , and tnf-α/β expression, declined or fluctuated, suggesting that sustained low temperature alters skin physiological status. This study provides physiological, biochemical, and molecular data that contribute to understanding low-temperature responses in juvenile yellowfin tuna.